The production of many commercially valuable rare earth oxides, or rare earth metal compounds, from mineral ores such as monazite includes first mining the ore, beneficiation of the ore, and subsequent chemical treatment of the ore to recover the rare earth content, which typically ranges from 1% to sometimes in excess of 10% mixed rare earth content. The chemical treatment step is utilized to convert metal species in the mineral ore to metal species which are soluble in aqueous systems so that the metal values may be separated out by solvent extraction systems and the like.
The entire cost of mining a mineral ore with 1% to greater than 10% rare earth content and the subsequent chemical treatment and separation of the rare earth materials is tied directly to the rare earth material; conversely on the order of 90% to 99% of the material processed in a typical approach to rare earth recovery is generated as a waste or slag product.
It is well known that many phosphate rock deposits contain rare earths and that a portion of these materials are dissolved during the processing of the rock to produce a wet-process phosphoric acid. In this case, the primary component of interest is the phosphate value, which is then used to produce various phosphate products, e.g. diammonium phosphate fertilizer. The cost of mining, beneficiation, and subsequent processing is associated with the phosphate content. Thus any rare earth dissolved into the acid has essentially no cost associated with it since it currently remains in the phosphoric acid.
While recovery of the rare earths from phosphoric acid would be attractive, to date there has not been an effective processing technology that would extract the rare earth materials from the phosphoric acid in a cost-effective manner. Thus, it would be valuable to find a method to recover rare earth materials from a primary phosphoric acid stream where the cost of mining, benefaction and chemical treatment was borne entirely by the principle phosphoric acid product.